With this technology, an HFC centralised DX system is used for MT loads and the LT system has a separate circuit that discharges its heat into the suction stage of the MT system.

The LT circuit has a low condensation temperature so R744 (CO2) can be applied in subcritical mode without excessive pressures. The challenges are not fundamentally different from systems with conventional refrigerants. The discharge pressure (at around 30 to 35 bar) is still within the normal design limits for refrigeration pipe work and components (typically 40 bar).

The temperature difference required to drive the heat transfer across this extra heat exchanger represents a slight loss in energy efficiency compared to a DX system.